Cemented carbide composition



Patented Oct. 18, 1938 CEMENTED CARBIDE COM'PO SKTION George Lucas, Euclid, Ohio, assignor to General Electric Company, a corporation of New York No Drawing Application April 17, 1937, Serial No. 137,551

9 Claims.

The present invention relates to slntered hard metal carbide compositions and more particularly to slntered hard metal compositions containing chromium or chromium carbide as an essential ingredient. Sintered hard metal compositions suitable for use as metal cutting tools usually consist of tungsten carbide with a binder metal of the iron group, for example cobalt, the binder generally comprising from about 2 to 25% by weight of the composition. Tools of thischaracter when containing about 5% cobalt have an average Rockwell A hardness of 92.2 and an average strength in the neighborhood of 215,000 lbs. per square inch. The strength and hardness however may vary with variations in the cobalt content of the alloy.

Heretofore attempts have been made to employ chromium in cemented carbide compositions. In some cases the chromium has been employed with the cobalt or other metal of the iron group as a binder medium for the tungsten carbide and in some cemented carbides chromium in the form of chromium carbide has been employed with tungsten carbide and a binder metal. So far as I am aware slntered hard metal compositions containing chromium or chromium carbide have never been employed on a commercial scale. This is due principally to the fact that although the addition of such ingredients usually increases the hardness of cemented carbide compositions they at the same time efiect such a reduction in the strength of the cemented carbide as to make it of little comparative value as a metal cutting tool. For example, a sintered metal cutting tool having the composition of WC, 27% TaC and 13% Co has an average Rockwell A hardness of 86.9 and an average strength. of 260,000 lbs.

per square inch. By substituting 3% chromium carbide (Grace) for 3% of the WC in the above composition, the Rockwell A hardness may be increased to 89 but the strength is reduced to about 167,000 lbs. per square inch.

It is one of the objects of the present invention to provide a slntered hard metal composition containing chromium which not only has a high degree of hardness but which in addition has a high degree of strength. In every case the figures indicating hardness and strength are average figures.

The novel features which are characteristic of my invention are set forth with particularity in the appended claims. My invention itself however will best be understood from reference to the following specification.

In carrying out my invention, I add a very small quantity of chromium carbide to 9. ccmented carbide composition. I have found that if the chromium carbide is added with certain limits that the hardness of the resulting cemented carbide is materially increased while the strength of the resulting cemented carbide is not adversely afiected and may even be increased. The quantity of chromium carbide (CrsCz) which may be employed to advantage in cemented carbide compositions is limited to appreciable quantities which however are for most purposes less than 1% by weight of the total content of the alloy. Very good results have been obtained with a quantity of chromium carbide varying from about .25% to 50% of the total content of the composition. For example, a sintered composition containing 93.7% tungsten carbide .25% chromium carbide and 6% cobalt has a Rockwell A hardness of 92.7 and a strength of about 229,000 lbs. per square inch, whereas a similar composition containing no chromium carbide has a hardness of about 92.2 and a strength of about 215,000 lbs. per square inch. Likewise, the composition consisting of 8'7 tungsten carbide and 13% cobalt has a Rockwell A hardness of 89.1 and a strength of 294,000 lbs. per square inch while a similar composition consisting of 86.75% tungsten carbide, .25% chromium carbide and 13% cobalt has a Rockwell A hardness of 89.8 and a strength of 302,000 lbs.- per square inch.

The addition of chromium or chromium carbide, withln the percentage range indicated herein, to cemented carbide cutting tools or wearresisting parts adds greatly to their efliciency. This is particularly true with respect to wire drawing dies. For example, cemented carbide wire drawing dies containing a small percentage of chromium, as herein disclosed, have given an average production of about 2950 lbs. of material, whereas the average production of cemented carbide dies containing no chromium but otherwise having the same composition as the first mentioned dies is only about 2125 lbs'. of ma terial.

The addition of chromium carbide is not only efiective in increasing the hardness and efficiency of sintered compositions consisting of tungsten carbide and cobalt without adversely afiecting their strength but in the limited range indicated is effective also in increasing the hardness and eificiency of other assembled carbide compositions without adversely affecting their strength, for example cemented carbide compositions consisting of tungsten carbide. tantalum carbide and a binder metal, compositions consisting of tungsten carbide, titanium carbide and a binder metal, or compositions consisting of the three carbides mentioned with a binder metal.

While the most satisfactory results are obtained by the use of small quantities of chromium carbide in cemented carbide compositions, chromium alone within the range indicated, 1. e from an appreciable quantity up to about 1% also provides an increase in the hardness without impairing the strength of the cemented carbide composition.

What I claim as new and desire to secure b Letters Patent of the United States is:

1. A cemented carbide composition containing an appreciable amount but less than 1% of chromium carbide the remainder of said composition consisting of about 2 to 25% cobalt and carbide material from the group tungsten carbide, tantalum carbide, titanium carbide.

2. A cemented carbide composition containing about .25% to of chromium carbide the remainder of said composition consisting of about 2 to 25% cobalt and carbide material from the group tungsten carbide, tantalum carbide, titanium carbide.

3. A cemented carbide composition containing about 2 to 25% cobalt, an appreciable quantity but less than 1% of chromium carbide, with the remainder substantially tungsten carbide.

, metal carbide particles from the group tungsten carbide, tantalum carbide, titanium carbide and about 2 to 25% cobalt.

7. A slntered' composition containing about 25% to .50% chromium carbide, about 2 to 25% cobalt, the remainder consisting of a mixture of tungsten carbide, tantalum carbide and titanium carbide.

8. A sintered composition containing about 25% to 50% chromium carbide, about 2 to 25% cobalt, the remainder consisting of a mixture of tungsten carbide and tantalum carbide. 9. A sintered composition containing about .25% to 50% chromium carbide, about 2 to 25% cobalt, the remainder consisting of a mixture of tungsten carbide and titanium carbide.

GEORGE LUCAS. 31 

